This invention relates generally to cathode ray tube (CRT) production and particularly to a readily changeable getter flashing device for such production.
During the manufacture of a cathode ray tube (CRT) a getter is disposed within the tube. The getter includes a metallic container held at one end of an elongated resilient spring whereby the getter extends into a funnel portion of the tube. After the tube is exhausted of gases and hermetically sealed, the getter material is quickly heated to vaporize, or flash, and deposit a film of getter material on the internal surface of the tube. The getter material, typically a barium aluminum alloy, has the property of sorbing gases which remain after the tube is exhausted, or gases which are later released by the walls and other structural components within the tube. The getter material, in effect, acts as an auxiliary pump to provide the high vacuum needed for effective tube operation.
The getter material is flashed by positioning a radio frequency (rf) coil in the proximity of the getter. In order to optimize vaporization of the getter material, the heating coil must be properly located and oriented with respect to the getter. Accordingly, the planes of the getter and the coil should be parallel and the coil and getter should be centered. The coil location and orientation are critical because the power delivered to the getter container varies with the inverse square of the distance between the coil and the container. Planar alignment between the getter and the coil is also critical to assure the proper interception of the transverse electrical field which heats the getter material. Improper orientation or location of the heater coil can cause severe localized heating and melt, or soften, the getter container, or the support spring and result in an unsatisfactory getter flash.
Typically CRT's are identified by a deflection angle, such as 90.degree., 100.degree. or 110.degree.. The deflection angle is the total angle through which the electron beam is horizontally scanned during the operation of the tube. For tubes of a particular deflection angle, the getters ordinarily are located at substantially the same location within the tubes. For this reason is possible to accurately orient and locate the getter in the proximity of the heating coil without attempting to detect the location of the getter. However, CRT's with different deflection angles typically have the getter located at different locations within the tube. For this reason as different tubes come down an assembly line it is necessary to change the getter flashing device in order to properly locate and orient the getters with respect to the heating coils. For this reason, there is a need for a getter flashing device which permits the rapid and ready changing of the tube orientating and locating mechanism while permitting the accurate location and orientation of the tubes with respect to the flashing coil. The present invention fulfills this need.